Current refrigeration trends promote the use of carbon dioxide and other types of natural refrigerants as opposed to conventional hydrofluorocarbon based refrigerants. Although such carbon dioxide based refrigeration systems may be considered more environmentally friendly, such systems may be somewhat less efficient. Specifically, the carbon dioxide based refrigeration systems may require more overall power usage given a lower critical point and therefore higher throttling losses between the heat rejection and heat absorption processes as compared to a conventional refrigeration cycle.
In a transcritical carbon dioxide refrigeration system, the gaseous refrigerant may be cooled in a gas cooler to a temperature that is still above the critical point. The carbon dioxide refrigerant then may be discharged to a flash tank where the refrigerant may be expanded and separated into liquid and vapor. Such transcritical carbon dioxide refrigeration systems, however, may have a disadvantage during warmer months due to excessive vapor or flash gas generation during the expansion process in the flash tank. Accommodating this excessive flash gas generation may reduce overall refrigeration system efficiency and/or require the use of additional components and the related costs.
There is thus a desire for a refrigeration system using natural refrigerants such as carbon dioxide with improved efficiency. Preferably, such an improved refrigeration system may be environmentally friendly but with reduced overall operational and maintenance requirements and costs.